docs: def check_rates(self, rates, base):
          """Local helper function for validating rates response"""
  
          if "rates" not in rates:
              raise RuntimeError("%s: 'rates' not found in results" % self.name)
          if "base" not in rates or rates["base"] != base or base not in rates["rates"]:
              self.log(logging.WARNING, "%s: 'base' not found in results", self.name)
          self.rates = rates